I had that problem as well, here's what I did to resolve it:
1: make sure borders touch other borders you've drawn, or shoreline.
2: keep the border solid, I think it interprets dotted lines as having openings still, perhaps after you fill the shape in you can change the border line to a more fun dotted-dashed pattern?
paging @Upvoteanthology
Okay, everything you've said is right, but there's slightly more to take into consideration. What you'll want to do is this:
Let's say I wanted to make an island off the coast of this map I'm working on.
Let's also say, that in this case, the island is sinking, and I wanted to represent that by using a dotted line do represent the coast.
So, I take out my bucket tool, choose the color I want, and click. But then this happens:
Oops, looked like I fucked up. But once I make it into a solid line, then it works! (TIP: If you're looking to fill in something that has dotted lines on any of its edges, you'll want to make it solid for the filling process! Change it back LATER!)
But now, let's say I wanted to create another, smaller island. This new island is way more jagged, and I want to represent its small size by using a really really thin line for some reason.
So, I go to fill it in again, the same way I did last time, but this happens:
Ugh. Not a good fill job
at all. So, this is the kicker. You'll want to go to the top of your document, where all the numbers are regarding the fill bucket (as you can see in the image below). Look at the number next to the "grow/shrink" box. If it's 0.75, it will fill 0.75 pixels outside of the box in which it's trying to fill. If you have a line that's 1px thick, you'll want around 1px or less of growth if you want a clean fill. 0px, and you'll get a messy job unless you zoom in enough for the app to comprehend every little nook and cranny. Note that in order to get a clear fill, you have to zoom in close, no matter what the growth number is.
With the island I made, 0.75px is a bit too large, and I ended up both lowering the amount of growth and making the line thicker to compensate. When you're making your own maps, you'll have to just find a number that works the majority of the time and change it when need be. Mine tends to be around 1.1px, since the majority of my lines are thicker than that.
Okay, so you've done it! You've filled it in! But now, if you did the same thing many people do, it might look like this:
Have no fear! Just move the painted regions onto another layer, then move the layer BELOW the outline of the island.
There we go, that's a bit better (again, it's a bit rough, but you get the idea
)!
And BAM! There you go! Two filled in islands that look okay! Now, I had a few more problems with filling when I was a beginner, so here's a little extra FAQ:
What does it mean when it says something like "Area not bounded, cannot fill", even though I have a boundary around my object?
That means you've zoomed in too far, so Inkscape doesn't recognize that there's a boundary there at all. What you'll want to do in this situation is go to the edge of your object and find a place where you can start filling from there. Once you find a place that it allows you to fill in, just work your way around the edges
I zoomed in, and it only filled in half the object. Once I fill in the rest of the island, I have two different fills which makes it so much harder to work with! Help???
Again, Inkscape doesn't understand there's an edge to your object, so it only fills in what it "sees"; your window, and a little bit outside of your window. All you have to do in that situation is go around the rest of your island and fill in the spaces that it can't do in one felt swoop. Then, you want to select all of the mini-fills, then go to Path-->Combine. This should combine all the mini-fills together into one!
ONE FINAL TIP: Try not to have a stroke paint around your fills. Strokes are best when they're separate from the fill altogether. There are some situations where having a stroke around the fill can be good, but when you combine multiple fills it ends up looking really really horrible.
HAPPY FILLING!
PS: Sorry it was so bad grammar-wise, I have a hard time explaining things clearly and concisely ;-;